1. Field of the Invention
The present invention relates to a process for cleaning a silicon surface, and more particularly to a process for cleaning a silicon surface in the TFT fabrication process for a TFT-LCD.
2. Description of the Prior Art
In the semiconductor IC and TFT-LCD array fabrication processes, the result of cleaning a silicon material plays an important role in the ultimate quality of IC devices and TFT arrays.
In the semiconductor IC fabrication process, Caros (H2SO4/H2O2), SC1 (standard clean 1; NH4OH/H2O2) and SC2 (standard clean 2; HCl/H2O2) cleaning methods have been extensively used for cleaning silicon wafers. These cleaning methods produce good cleaning results, but suffer from requiring a large amount of chemicals, resulting in environmental problems and additional treatment costs. In addition, ozone and HF have also been used to clean silicon wafers. For example, in U.S. Patent Application Publication No. 2001/0017143 A1, ozone water and HF are used to clean semiconductor silicon wafers. In U.S. Pat. No. 6,240,933, the semiconductor silicon wafer is first cleaned with ozone water and then the oxide is removed by vapor. In U.S. Pat. No. 6,348,157, the semiconductor is cleaned using ozone water, HF (with megasonic), deionized water (DIW), HF and DIW in sequence.
In the amorphous TFT-LCD fabrication process, amorphous silicon cleaning is conducted using CJ (cavitation-jet), a brush, ozone water, or UV ozone. CJ and brush cleaning are ineffective on particles smaller than 1 μm. If the ozone water concentration is too low (<10 ppm), the cleaning is ineffective. UV ozone provides a relatively good rate of removal for organic material, but a relatively poor rate of removal for metal contaminants.
Polysilicon TFT has higher electron mobility, quicker response time, and higher resolution than amorphous TFT. Therefore, polysilicon TFT has been extensively applied to drive LCDs. Generally, polysilicon TFT fabrication uses a low temperature polysilicon (LTPS) process. That is, amorphous silicon is first formed, and is then subjected to laser annealing to form polysilicon.
There is a need to develop an effective cleaning process for silicon wafer in semiconductor IC and for amorphous silicon and polysilicon in TFT-LCDs.